This paper documents a laboratory experiment that analyses voter participation in common interest proportional representation (PR) elections, comparing this with majority rule. Consistent with theoretical predictions, poorly informed voters in either system abstain from voting, thereby shifting weight to those who are better informed. A dilution problem makes mistakes especially costly under PR, so abstention is higher in PR in contrast with private interest environments, and welfare is lower. Deviations from Nash equilibrium predictions can be accommodated by a logit version of quantal response equilibrium (QRE), which allows for voter mistakes.